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The documentation could confuse people to expect that CPU models with usable='no' attribute are not usable at all on the current host. But they cannot be only used without explicitly disabling some features. Signed-off-by: Jiri Denemark <jdenemar@redhat.com> Reviewed-by: Andrea Bolognani <abologna@redhat.com>
604 lines
21 KiB
XML
604 lines
21 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>Domain capabilities XML format</h1>
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<ul id="toc"></ul>
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<h2><a id="Overview">Overview</a></h2>
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<p>Sometimes, when a new domain is to be created it may come handy to know
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the capabilities of the hypervisor so the correct combination of devices and
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drivers is used. For example, when management application is considering the
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mode for a host device's passthrough there are several options depending not
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only on host, but on hypervisor in question too. If the hypervisor is qemu
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then it needs to be more recent to support VFIO, while legacy KVM is
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achievable just fine with older qemus.</p>
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<p>The main difference between
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<a href="/html/libvirt-libvirt-host.html#virConnectGetCapabilities">
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<code>virConnectGetCapabilities</code>
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</a>
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and the emulator capabilities API is, the former one aims more on
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the host capabilities (e.g. NUMA topology, security models in
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effect, etc.) while the latter one specializes on the hypervisor
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capabilities.</p>
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<p>While the <a href="formatcaps.html">Driver Capabilities</a> provides the
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host capabilities (e.g NUMA topology, security models in effect, etc.), the
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Domain Capabilities provides the hypervisor specific capabilities for
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Management Applications to query and make decisions regarding what to
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utilize.</p>
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<p>The Domain Capabilities can provide information such as the correct
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combination of devices and drivers that are supported. Knowing which host
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and hypervisor specific options are available or supported would allow the
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management application to choose an appropriate mode for a pass-through
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host device as well as which adapter to utilize.</p>
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<p>Some XML elements may be entirely omitted from the domaincapabilities
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XML, depending on what the libvirt driver has filled in. Applications
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should only act on what is explicitly reported in the domaincapabilities
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XML. For example, if <disk supported='yes'/> is present, you can safely
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assume the driver supports <disk> devices. If <disk supported='no'/> is
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present, you can safely assume the driver does NOT support <disk>
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devices. If the <disk> block is omitted entirely, the driver is not
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indicating one way or the other whether it supports <disk> devices, and
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applications should not interpret the missing block to mean any thing in
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particular.</p>
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<h2><a id="elements">Element and attribute overview</a></h2>
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<p> A new query interface was added to the virConnect API's to retrieve the
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XML listing of the set of domain capabilities (<span class="since">Since
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1.2.7</span>):</p>
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<pre>
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<a href="/html/libvirt-libvirt-domain.html#virConnectGetDomainCapabilities">virConnectGetDomainCapabilities</a>
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</pre>
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<p>The root element that emulator capability XML document starts with has
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name <code>domainCapabilities</code>. It contains at least four direct
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child elements:</p>
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<pre>
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<domainCapabilities>
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<path>/usr/bin/qemu-system-x86_64</path>
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<domain>kvm</domain>
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<machine>pc-i440fx-2.1</machine>
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<arch>x86_64</arch>
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...
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</domainCapabilities>
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</pre>
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<dl>
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<dt><code>path</code></dt>
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<dd>The full path to the emulator binary.</dd>
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<dt><code>domain</code></dt>
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<dd>Describes the <a href="formatdomain.html#elements">virtualization
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type</a> (or so called domain type).</dd>
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<dt><code>machine</code></dt>
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<dd>The domain's <a href="formatdomain.html#elementsOSBIOS">machine
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type</a>. Since not every hypervisor has a sense of machine types
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this element might be omitted in such drivers.</dd>
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<dt><code>arch</code></dt>
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<dd>The domain's <a href="formatdomain.html#elementsOSBIOS">
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architecture</a>.</dd>
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</dl>
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<h3><a id="elementsCPUAllocation">CPU Allocation</a></h3>
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<p>Before any devices capability occurs, there might be info on domain
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wide capabilities, e.g. virtual CPUs:</p>
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<pre>
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<domainCapabilities>
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...
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<vcpu max='255'/>
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...
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</domainCapabilities>
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</pre>
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<dl>
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<dt><code>vcpu</code></dt>
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<dd>The maximum number of supported virtual CPUs</dd>
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</dl>
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<h3><a id="elementsOSBIOS">BIOS bootloader</a></h3>
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<p>Sometimes users might want to tweak some BIOS knobs or use
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UEFI. For cases like that, <a
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href="formatdomain.html#elementsOSBIOS"><code>os</code></a>
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element exposes what values can be passed to its children.</p>
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<pre>
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<domainCapabilities>
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...
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<os supported='yes'>
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<enum name='firmware'>
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<value>bios</value>
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<value>efi</value>
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</enum>
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<loader supported='yes'>
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<value>/usr/share/OVMF/OVMF_CODE.fd</value>
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<enum name='type'>
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<value>rom</value>
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<value>pflash</value>
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</enum>
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<enum name='readonly'>
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<value>yes</value>
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<value>no</value>
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</enum>
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<enum name='secure'>
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<value>yes</value>
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<value>no</value>
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</enum>
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</loader>
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</os>
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...
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<domainCapabilities>
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</pre>
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<p>The <code>firmware</code> enum corresponds to the
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<code>firmware</code> attribute of the <code>os</code> element in
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the domain XML. The presence of this enum means libvirt is capable
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of the so-called firmware auto-selection feature. And the listed
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firmware values represent the accepted input in the domain
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XML. Note that the <code>firmware</code> enum reports only those
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values for which a firmware "descriptor file" exists on the host.
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Firmware descriptor file is a small JSON document that describes
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details about a given BIOS or UEFI binary on the host, e.g. the
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fimware binary path, its architecture, supported machine types,
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NVRAM template, etc. This ensures that the reported values won't
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cause a failure on guest boot.
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</p>
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<p>For the <code>loader</code> element, the following can occur:</p>
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<dl>
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<dt><code>value</code></dt>
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<dd>List of known firmware binary paths. Currently this is used
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only to advertise the known location of OVMF binaries for
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QEMU. OVMF binaries will only be listed if they actually exist on
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host.</dd>
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<dt><code>type</code></dt>
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<dd>Whether the boot loader is a typical BIOS (<code>rom</code>)
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or a UEFI firmware (<code>pflash</code>). Each <code>value</code>
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sub-element under the <code>type</code> enum represents a possible
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value for the <code>type</code> attribute for the <loader/>
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element in the domain XML. E.g. the presence
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of <code>pfalsh</code> under the <code>type</code> enum means that
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a domain XML can use UEFI firmware via: <loader/>
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type="pflash" ...>/path/to/the/firmware/binary/</loader>.
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</dd>
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<dt><code>readonly</code></dt>
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<dd>Options for the <code>readonly</code> attribute of the
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<loader/> element in the domain XML.</dd>
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<dt><code>secure</code></dt>
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<dd>Options for the <code>secure</code> attribute of the
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<loader/> element in the domain XML. Note that the
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value <code>yes</code> is listed only if libvirt detects a
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firmware descriptor file that has path to an OVMF binary that
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supports Secure boot, and lists its architecture and supported
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machine type.</dd>
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</dl>
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<h3><a id="elementsCPU">CPU configuration</a></h3>
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<p>
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The <code>cpu</code> element exposes options usable for configuring
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<a href="formatdomain.html#elementsCPU">guest CPUs</a>.
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</p>
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<pre>
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<domainCapabilities>
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...
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<cpu>
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<mode name='host-passthrough' supported='yes'/>
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<mode name='host-model' supported='yes'>
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<model fallback='allow'>Broadwell</model>
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<vendor>Intel</vendor>
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<feature policy='disable' name='aes'/>
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<feature policy='require' name='vmx'/>
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</mode>
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<mode name='custom' supported='yes'>
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<model usable='no'>Broadwell</model>
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<model usable='yes'>Broadwell-noTSX</model>
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<model usable='no'>Haswell</model>
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...
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</mode>
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</cpu>
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...
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<domainCapabilities>
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</pre>
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<p>
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Each CPU mode understood by libvirt is described with a
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<code>mode</code> element which tells whether the particular mode
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is supported and provides (when applicable) more details about it:
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</p>
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<dl>
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<dt><code>host-passthrough</code></dt>
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<dd>No mode specific details are provided.</dd>
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<dt><code>host-model</code></dt>
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<dd>
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If <code>host-model</code> is supported by the hypervisor, the
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<code>mode</code> describes the guest CPU which will be used when
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starting a domain with <code>host-model</code> CPU. The hypervisor
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specifics (such as unsupported CPU models or features, machine type,
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etc.) may be accounted for in this guest CPU specification and thus
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the CPU can be different from the one shown in host capabilities XML.
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This is indicated by the <code>fallback</code> attribute of the
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<code>model</code> sub element: <code>allow</code> means not all
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specifics were accounted for and thus the CPU a guest will see may
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be different; <code>forbid</code> indicates that the CPU a guest will
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see should match this CPU definition.
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</dd>
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<dt><code>custom</code></dt>
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<dd>
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The <code>mode</code> element contains a list of supported CPU
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models, each described by a dedicated <code>model</code> element.
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The <code>usable</code> attribute specifies whether the model can
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be used directly on the host. When usable='no' the corresponding model
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cannot be used without disabling some features that the CPU of such
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model is expected to have. A special value <code>unknown</code>
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indicates libvirt does not have enough information to provide the
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usability data.
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</dd>
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</dl>
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<h3><a id="elementsIothreads">I/O Threads</a></h3>
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<p>
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The <code>iothread</code> elements indicates whether or not
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<a href="formatdomain.html#elementsIOThreadsAllocation">I/O threads</a>
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are supported.
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</p>
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<pre>
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<domainCapabilities>
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...
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<iothread supported='yes'/>
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...
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<domainCapabilities>
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</pre>
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<h3><a id="elementsDevices">Devices</a></h3>
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<p>
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Another set of XML elements describe the supported devices and their
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capabilities. All devices occur as children of the main
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<code>devices</code> element.
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</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<disk supported='yes'>
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<enum name='diskDevice'>
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<value>disk</value>
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<value>cdrom</value>
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<value>floppy</value>
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<value>lun</value>
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</enum>
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...
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</disk>
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<hostdev supported='no'/>
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</devices>
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</domainCapabilities>
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</pre>
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<p>Reported capabilities are expressed as an enumerated list of available
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options for each of the element or attribute. For example, the
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<disk/> element has an attribute <code>device</code> which can
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support the values <code>disk</code>, <code>cdrom</code>,
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<code>floppy</code>, or <code>lun</code>.</p>
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<h4><a id="elementsDisks">Hard drives, floppy disks, CDROMs</a></h4>
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<p>Disk capabilities are exposed under the <code>disk</code> element. For
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instance:</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<disk supported='yes'>
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<enum name='diskDevice'>
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<value>disk</value>
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<value>cdrom</value>
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<value>floppy</value>
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<value>lun</value>
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</enum>
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<enum name='bus'>
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<value>ide</value>
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<value>fdc</value>
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<value>scsi</value>
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<value>virtio</value>
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<value>xen</value>
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<value>usb</value>
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<value>sata</value>
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<value>sd</value>
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</enum>
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</disk>
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...
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</devices>
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</domainCapabilities>
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</pre>
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<dl>
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<dt><code>diskDevice</code></dt>
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<dd>Options for the <code>device</code> attribute of the <disk/>
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element.</dd>
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<dt><code>bus</code></dt>
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<dd>Options for the <code>bus</code> attribute of the <target/>
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element for a <disk/>.</dd>
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</dl>
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<h4><a id="elementsGraphics">Graphical framebuffers</a></h4>
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<p>Graphics device capabilities are exposed under the
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<code>graphics</code> element. For instance:</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<graphics supported='yes'>
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<enum name='type'>
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<value>sdl</value>
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<value>vnc</value>
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<value>spice</value>
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</enum>
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</graphics>
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...
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</devices>
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</domainCapabilities>
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</pre>
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<dl>
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<dt><code>type</code></dt>
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<dd>Options for the <code>type</code> attribute of the <graphics/>
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element.</dd>
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</dl>
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<h4><a id="elementsVideo">Video device</a></h4>
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<p>Video device capabilities are exposed under the
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<code>video</code> element. For instance:</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<video supported='yes'>
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<enum name='modelType'>
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<value>vga</value>
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<value>cirrus</value>
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<value>vmvga</value>
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<value>qxl</value>
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<value>virtio</value>
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</enum>
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</video>
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...
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</devices>
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</domainCapabilities>
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</pre>
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<dl>
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<dt><code>modelType</code></dt>
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<dd>Options for the <code>type</code> attribute of the
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<video><model> element.</dd>
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</dl>
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<h4><a id="elementsHostDev">Host device assignment</a></h4>
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<p>Some host devices can be passed through to a guest (e.g. USB, PCI and
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SCSI). Well, only if the following is enabled:</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<hostdev supported='yes'>
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<enum name='mode'>
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<value>subsystem</value>
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<value>capabilities</value>
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</enum>
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<enum name='startupPolicy'>
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<value>default</value>
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<value>mandatory</value>
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<value>requisite</value>
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<value>optional</value>
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</enum>
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<enum name='subsysType'>
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<value>usb</value>
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<value>pci</value>
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<value>scsi</value>
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</enum>
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<enum name='capsType'>
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<value>storage</value>
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<value>misc</value>
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<value>net</value>
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</enum>
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<enum name='pciBackend'>
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<value>default</value>
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<value>kvm</value>
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<value>vfio</value>
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<value>xen</value>
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</enum>
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</hostdev>
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</devices>
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</domainCapabilities>
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</pre>
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<dl>
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<dt><code>mode</code></dt>
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<dd>Options for the <code>mode</code> attribute of the <hostdev/>
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element.</dd>
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<dt><code>startupPolicy</code></dt>
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<dd>Options for the <code>startupPolicy</code> attribute of the
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<hostdev/> element.</dd>
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<dt><code>subsysType</code></dt>
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<dd>Options for the <code>type</code> attribute of the <hostdev/>
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element in case of <code>mode="subsystem"</code>.</dd>
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<dt><code>capsType</code></dt>
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<dd>Options for the <code>type</code> attribute of the <hostdev/>
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element in case of <code>mode="capabilities"</code>.</dd>
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<dt><code>pciBackend</code></dt>
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<dd>Options for the <code>name</code> attribute of the <driver/>
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element.</dd>
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</dl>
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<h4><a id="elementsRNG">RNG device</a></h4>
|
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<p>RNG device capabilities are exposed under the
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<code>rng</code> element. For instance:</p>
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<pre>
|
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<domainCapabilities>
|
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...
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<devices>
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<rng supported='yes'>
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<enum name='model'>
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<value>virtio</value>
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<value>virtio-transitional</value>
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<value>virtio-non-transitional</value>
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</enum>
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<enum name='backendModel'>
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<value>random</value>
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<value>egd</value>
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<value>builtin</value>
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</enum>
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</rng>
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...
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</devices>
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</domainCapabilities>
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</pre>
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<dl>
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<dt><code>model</code></dt>
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<dd>Options for the <code>model</code> attribute of the
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<rng> element.</dd>
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<dt><code>backendModel</code></dt>
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<dd>Options for the <code>model</code> attribute of the
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<rng><backend> element.</dd>
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</dl>
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<h3><a id="elementsFeatures">Features</a></h3>
|
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|
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<p>One more set of XML elements describe the supported features and
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their capabilities. All features occur as children of the main
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<code>features</code> element.</p>
|
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|
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<pre>
|
|
<domainCapabilities>
|
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...
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<features>
|
|
<gic supported='yes'>
|
|
<enum name='version'>
|
|
<value>2</value>
|
|
<value>3</value>
|
|
</enum>
|
|
</gic>
|
|
<vmcoreinfo supported='yes'/>
|
|
<genid supported='yes'/>
|
|
<backingStoreInput supported='yes'/>
|
|
<backup supported='yes'/>
|
|
<sev>
|
|
<cbitpos>47</cbitpos>
|
|
<reduced-phys-bits>1</reduced-phys-bits>
|
|
</sev>
|
|
</features>
|
|
</domainCapabilities>
|
|
</pre>
|
|
|
|
<p>Reported capabilities are expressed as an enumerated list of
|
|
possible values for each of the elements or attributes. For example, the
|
|
<code>gic</code> element has an attribute <code>version</code> which can
|
|
support the values <code>2</code> or <code>3</code>.</p>
|
|
|
|
<p>For information about the purpose of each feature, see the
|
|
<a href="formatdomain.html#elementsFeatures">relevant section</a> in
|
|
the domain XML documentation.
|
|
</p>
|
|
|
|
<h4><a id="elementsGIC">GIC capabilities</a></h4>
|
|
|
|
<p>GIC capabilities are exposed under the <code>gic</code> element.</p>
|
|
|
|
<dl>
|
|
<dt><code>version</code></dt>
|
|
<dd>Options for the <code>version</code> attribute of the
|
|
<code>gic</code> element.</dd>
|
|
</dl>
|
|
|
|
<h4><a id="elementsvmcoreinfo">vmcoreinfo</a></h4>
|
|
|
|
<p>Reports whether the vmcoreinfo feature can be enabled.</p>
|
|
|
|
<h4><a id="elementsgenid">genid</a></h4>
|
|
|
|
<p>Reports whether the genid feature can be used by the domain.</p>
|
|
|
|
<h4><a id="featureBackingStoreInput">backingStoreInput</a></h4>
|
|
|
|
<p>Reports whether the hypervisor will obey the <backingStore>
|
|
elements configured for a <disk> when booting the guest, hotplugging
|
|
the disk to a running guest, or similar.
|
|
</p>
|
|
|
|
<h4><a id="featureBackup">backup</a></h4>
|
|
|
|
<p>Reports whether the hypervisor supports the backup, checkpoint, and
|
|
related features. (<code>virDomainBackupBegin</code>,
|
|
<code>virDomainCheckpointCreateXML</code> etc). The presence of the
|
|
<code>backup</code> element even if <code>supported='no'</code> implies that
|
|
the <code>VIR_DOMAIN_UNDEFINE_CHECKPOINTS_METADATA</code> flag for
|
|
<code>virDomainUndefine</code> is supported.
|
|
</p>
|
|
|
|
<h4><a id="elementsSEV">SEV capabilities</a></h4>
|
|
|
|
<p>AMD Secure Encrypted Virtualization (SEV) capabilities are exposed under
|
|
the <code>sev</code> element.
|
|
SEV is an extension to the AMD-V architecture which supports running
|
|
virtual machines (VMs) under the control of a hypervisor. When supported,
|
|
guest owner can create a VM whose memory contents will be transparently
|
|
encrypted with a key unique to that VM.</p>
|
|
|
|
<p>
|
|
For more details on the SEV feature, please follow resources in the
|
|
AMD developer's document store. In order to use SEV with libvirt have
|
|
a look at <a href="formatdomain.html#launchSecurity">SEV in domain XML</a>
|
|
</p>
|
|
|
|
<dl>
|
|
<dt><code>cbitpos</code></dt>
|
|
<dd>When memory encryption is enabled, one of the physical address bits
|
|
(aka the C-bit) is utilized to mark if a memory page is protected. The
|
|
C-bit position is Hypervisor dependent.</dd>
|
|
<dt><code>reducedPhysBits</code></dt>
|
|
<dd>When memory encryption is enabled, we lose certain bits in physical
|
|
address space. The number of bits we lose is hypervisor dependent.</dd>
|
|
</dl>
|
|
|
|
</body>
|
|
</html>
|